1. Field of the Invention
The present invention relates to an image forming apparatus for forming an image wherein a toner image is formed on its toner image carrier and then, transferred onto a to-be-transferred body. More particularly, it relates to an image forming apparatus equipped with a temporarily-collecting member which temporarily collects post-transfer residual toner on the toner image carrier and expels the toner later.
2. Description of Related Art
An electro-photographic-type image forming apparatus forms a toner image on a toner image carrier by taking steps of charge, exposure, and development. The toner image is transferred onto a to-be-transferred body and fixed. In this way, an image is formed. There remains some toner on the toner image carrier after transfer of a toner image. The residual toner is termed as post-transfer residual toner, herein. The post-transfer residual toner is obstacle to charge and exposure. Furthermore, post-transfer residual toner distributes unevenly leaving last toner image pattern before transferred. Therefore, post-transfer residual toner causes noises to next image formation.
Therefore, there has been devised an image forming apparatus equipped with a cleaner at a position after image transfer and before charge as disclosed in JP Laid-open Patent Publication No. 2001-255799. However, in case a cleaner is employed, collected post-transfer residual toner becomes waste toner. This is unfavorable in terms of environmental preservation. Therefore, there has been proposed an image forming apparatus without a cleaner such as disclosed in JP Laid-open Patent Publication No. 2002-372878. In such an image forming apparatus without a cleaner, post-transfer residual toner is collected by a developer. For surely collecting post-transfer residual toner by a developer, it is required to control charge quantity of the post-transfer residual toner. For that purpose, the image forming apparatus disclosed in the Publication No. 2002-372878 is equipped with a temporarily-collecting member (brush roll) which temporarily collects post-transfer residual toner and gives it back to an image carrier at a position after image transfer and before charge. The temporarily-collecting member is applied with an appropriate level of voltage. Therefore, post-transfer residual toner of which charge quantity is adjusted should be returned to the image carrier.
However, the above-mentioned conventional image forming apparatus without a cleaner has had the following problem. That is, adequate charge adjustment cannot always be done by just applying voltage to the temporarily-collecting member and its case. Subsequently, there occur problems such that toner accumulates in the temporarily-collecting member, charge quantity of toner returned to the image carrier is not appropriate, and the like. For resolving such problems, it has been attempted that the temporarily-collecting member is made to get contact with an appropriate electrode and voltage is applied thereto. However, as long as a contact area of the temporarily-collecting member and the electrode is not taken to some extent, a sufficient effect of it cannot be expected. On the other hand, making a contact area large causes a situation that an electrode is pushed in the temporarily-collecting member strongly. As a result, deformation and wear-out occur at the temporarily-collecting member, which are problematic.